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arXiv · 2009.01241

A Relationship Between Stellar Metallicity Gradients and Galaxy Age in Dwarf Galaxies

Francisco J. Mercado·James S. Bullock·Michael Boylan-Kolchin·Jorge Moreno·Andrew Wetzel·Kareem El-Badry·Andrew S. Graus·Alex Fitts·Philip F. Hopkins·Claude-André Faucher-Giguère
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Abstract

We explore the origin of stellar metallicity gradients in simulated and observed dwarf galaxies. We use FIRE-2 cosmological baryonic zoom-in simulations of 26 isolated galaxies as well as existing observational data for 10 Local Group dwarf galaxies. Our simulated galaxies have stellar masses between $10^{5.5}$ and $10^{8.6} \msun$. Whilst gas-phase metallicty gradients are generally weak in our simulated galaxies, we find that stellar metallicity gradients are common, with central regions tending to be more metal-rich than the outer parts. The strength of the gradient is correlated with galaxy-wide median stellar age, such that galaxies with younger stellar populations have flatter gradients. Stellar metallicty gradients are set by two competing processes: (1) the steady "puffing" of old, metal-poor stars by feedback-driven potential fluctuations, and (2) the accretion of extended, metal-rich gas at late times, which fuels late-time metal-rich star formation. If recent star formation dominates, then extended, metal-rich star formation washes out pre-existing gradients from the "puffing" process. We use published results from ten Local Group dwarf galaxies to show that a similar relationship between age and stellar metallicity-gradient strength exists among real dwarfs. This suggests that observed stellar metallicity gradients may be driven largely by the baryon/feedback cycle rather than by external environmental effects.

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Francisco J. Mercado, James S. Bullock, Michael Boylan-Kolchin, Jorge Moreno, Andrew Wetzel, Kareem El-Badry, Andrew S. Graus, Alex Fitts, Philip F. Hopkins, Claude-André Faucher-Giguère. 2020-09-02. A Relationship Between Stellar Metallicity Gradients and Galaxy Age in Dwarf Galaxies. https://doi.org/10.1093/mnras/staa3958

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